Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$144.84	11.311%	$161.2229	$161.22	$161.20	$161.20
Purchase #2	$243.42	7.232%	$261.0241	$261.02	$261.00	$261.00
Purchase #3	$27.71	6.317%	$29.4604	$29.46	$29.45	$29.50
Purchase #4	$132.74	7.114%	$142.1831	$142.18	$142.20	$142.20
Purchase #5	$54.51	13.167%	$61.6873	$61.69	$61.70	$61.70
Purchase #6	$168.35	3.290%	$173.8887	$173.89	$173.90	$173.90
Purchase #7	$141.81	6.362%	$150.832	$150.83	$150.85	$150.80
7 purchase totals =	$913.38		$980.2985	$980.29	$980.30	$980.30